1. Field of the Invention
The present invention relates to a particle size distribution measurement device to measure the particle size distribution of particles distributed within the dispersion medium.
2. Description of Related Art
The technology to measure particle size distribution is essential to determine and evaluate the performance of particulate matters throughout wide areas, such as drugs, food, ceramics, cosmetics, paint and coloring matter, and the importance has increased as time goes by. As a method to measure the particle size distribution of particulate matters, a laser diffraction/scattering particle size distribution measurement device already exists. For example, in the laser diffraction/scattering particle size distribution measurement device disclosed in Japanese Laid-Open Patent Application 2000-155088, sample particles are distributed and dispersed in a dispersion medium as a suspension, and this suspension is supplied to a flow cell; a laser beam is irradiated to the flow cell in a state where the suspension is in the flow cell. The laser beam diffracted and/or scattered by the particles in the suspension is detected by a detector, and the intensity of the obtained diffracted light and/or scattered light is processed based upon the Fraunhofer Diffraction Theory and the Mie Scattering Theory; and the particle diameter of the sample is obtained.
To supply this suspension to the flow cell, a circulation channel to circulate the suspension is established, and a circulation bath, where a sample is dispersed in a dispersion medium, and a circulation pump intervene in this circulation channel, and it is designed so that a dispersion medium sucked from a dispersion medium tank via a dispersion medium supply system is poured into the circulation bath.
However, in the related conventional dispersion medium supply system, since a pouring end is established in the upper position of the circulation bath and is designed to discharge the dispersion medium from the pouring end and to pour it into the circulation bath, there is the defect that a portion of air existing within the circulation channel is pushed deeper at the time of initial pouring, and that falling causes the mingling of the air at the time of supply, so that in either case, air easily remains within the circulation channel after pouring the dispersion medium. If air ventilation processing is sufficiently performed after pouring in order to cope with these defects, there is another problem of extending the preparation time, and it is also highly possible that even with air ventilation processing, bubbles may remain within the circulation channel, and the generation of unnecessarily scattering light by the bubbles causes a reduction of the S/N ratio.
Further, a water level sensor to detect a filled level and a shortage level is established in the circulation bath to prevent overflow and an abnormal shortage of the suspension. Therefore, the design secures pouring of the dispersion medium and appropriate circulation of the suspension. In order to appropriately obtain the particle diameter of a sample, it is important to accurately control the concentration of the suspension.
The above-mentioned Japanese Laid-Open Patent Application 2000-155088, to adjust the concentration of the suspension, ah inspection light is irradiated to a flow cell while the suspension is circulated within a circulation channel, and the concentration is determined based on the ratio between the quantity of the inspection light from a light source and the quantity of the transmitted light, in other words, based upon transmittance, and, for example, if it is determined that the concentration is high, it is designed to conduct the following procedure while repeating drainage and filling.
The suspension is drained by an appropriate amount from the circulation channel, and then the dispersion medium is supplied via the dispersion supply system until the water level sensor detects the filled level in the circulation bath. The suspension is then again circulated within the circulation channel in the filled state; and the concentration is determined according to the irradiation of the inspection light, making it difficult to adjust by delicate pouring, so accurate adjustment of the concentration is difficult. By the same token, there is the problem that high accuracy of measurement and reproducibility for the measurement of the particle size distribution cannot be obtained.